Developments in medicine have enabled the use of many non-classical surgical techniques in the treatment of diseases and disorders. For example, significant advances in implantable medical devices have enabled a host of new treatment options for patients. Early implantable medical devices were limited to surgical grade metals and were primarily used for gross mechanical repairs such as bone securement or replacement. However, in the last two decades, implantation of temporary or permanent structural and functioning elements has become commonplace, and such devices have become more intricate and complex in their structure and function.
While beneficial for treating a variety of medical conditions, the placement of metal or polymeric devices in the body can give rise to numerous complications. Some of these complications include increased risk of infection, initiation of a foreign body response (which can result in inflammation and/or fibrous encapsulation), and initiation of a wound healing response (which can result in hyperplasia).
One approach to reducing potential complications has been to explore the types of materials used to fabricate implantable medical devices. For example, implantable medical devices can be fabricated from polymeric materials (such as polyurethane) that are believed to be less likely to initiate adverse effects within the body.
Another approach to reducing the potential harmful effects that can result from medical device implantation is to provide biocompatible agents at tissue or blood-contacting surfaces of the implanted device. For example, heparin can be provided at a surface of a device to reduce thrombogenicity. One benefit of providing biocompatible agents at the surface of a device is the avoidance of toxic concentrations of drugs that are sometimes necessary, when given systemically, to achieve therapeutic concentrations at the site where they are required.
The term “implantation site” refers to the site within a patient's body at which the implantable device is placed according to the invention. This can be compared to the term “treatment site,” which can include the implantation site as well as the area of the body that is to receive treatment directly or indirectly from a device component. For example, in some instances, agents can migrate from the implantation site to areas surrounding the device itself, thereby treating a larger area than simply the implantation site. An example that illustrates this distinction can be seen in the use of drug-eluting stents (DES). These relatively recent devices can include bioactive agents that are eluted from the stent over time. Such eluted bioactive agents can provide treatment to the area of the body at the implantation site and beyond (the treatment site) as the agents migrate from the implantation site to areas surrounding the device itself.
Some treatments can require that a medical device, once implanted, reside in different physiological mileux within the body. In other words, once implanted, the device can come in contact with more than one distinct physiological environment. For example, one portion of the device may reside within a blood-contacting environment, while another portion of the device may reside within an extravascular environment, such as a tissue environment. The biocompatibility requirements for these different portions can be widely divergent.
On a separate subject, matrices that can be used for cell immobilization, tissue adherence, and controlled drug delivery in association with implantable devices have been described. See U.S. Pat. No. 6,007,833 (Chudzik et al., “Crosslinkable Macromers Bearing Initiator Groups”), U.S. Pat. No. 6,156,345 (Chudzik et al., “Crosslinkable Macromers Bearing Initiator Groups”), U.S. Pat. No. 6,410,044 (Chudzik et al., “Crosslinkable Macromers”), and U.S. Publication No. 2003/0031697 (Chudzik et al., “Crosslinkable Macromers”).